The present invention relates to a display device, and, more particularly, the invention relates to a display device in which noises and power consumption are reduced by optimizing a method for supplying display data to driver ICs mounted on the display device and by adopting a novel signal transmission circuit.
A liquid crystal display device operating on the basis a STN (Super Twisted Nematic) method or a TFT (Thin Film Transistor) method has been popularly used as a display device in a personal computer or the like. The liquid crystal display device includes a liquid crystal display panel and drive circuits which drive the liquid crystal display panel.
With respect to such a liquid crystal display device, there in a technique in which the drive circuit is formed as an integrated circuit on a silicon chip separately from the liquid crystal display panel, and the silicon chip in which the semiconductor circuit is formed is mounted on the liquid crystal display panel. As a method for mounting the silicon chip, there is a method in which a TCP (Tape Carrier Package) is used or a method in which a silicon chip is mounted on a transparent insulation substrate which forms a liquid crystal display panel, such as the so-called flip-chip method (FCA: Flip Chip Attachment) or COG (Chip On Glass) method.
In the typical liquid crystal display device, a signal is supplied through wiring formed in the printed wiring board. Further, the flip-chip method uses a so-called data sequential transmission method. In the data sequential transmission method, a signal is transmitted through wiring formed on the transparent insulation substrate, and signals are transmitted from one preceding silicon chip to a succeeding silicon chip.
Connection terminals (bumps) are formed on a silicon chip. In the flip-chip method, the connection terminals are electrically connected with electrodes on the transparent insulation substrate.
To drive circuits which are formed on the silicon chip, display data, control signals, power source voltages and the like are inputted from the outside through the connection terminals. The drive circuit outputs a drive signal, which is used to drive the liquid crystal display panel. In the data sequential transmission method, the drive circuit also outputs display data, control signals, power source voltages and the like for the next drive circuit through the wiring on the transparent insulated substrate.
For example, as a drive circuit which drives a TFT liquid crystal panel mounted on a notebook type computer or a liquid crystal display monitor, there is a drive circuit which rapidly inputs 6 bits for each of three dots of the three colors, consisting of red, blue and green (R, G, B), of one pixel, that is, 18 bits in total, and generates output voltages of 64 gray scale levels based on this digital data. In a data transmission method for an interface which uses CMOS circuits, an extremely rapid transmission and reception of signals is performed using 18 data lines and a drive frequency of 81 MHz.
Recently, in a liquid crystal display device, low voltage differential signals (LVDS) have been used as the signals which are inputted from an external device to realize an interface which transmits and receives digital data at a high speed. With the use of such low voltage differential signals, compared to the transmission method which uses CMOS circuits, it is expected that a reduction of the power consumption and an attenuation of the electromagnetic interference (EMI) by the input signals and the output signals can be achieved. Accordingly, in consideration of the current expectation that a liquid crystal panel for the next generation will demand higher definition and a larger screen, and that eventually the number of signal lines will be increased and the length of lines also will be increased, to solve drawbacks, such as an increase in the cost and a lowering of signal peak values, the use of low voltage differential signals has been proposed as a method for transmitting signals to the drive circuit and for receiving signals from the drive circuit in a liquid crystal display device.
Japanese Patent Laid-Open Publication No. H11(1999)-242463 discloses a technique for the use of low voltage differential signals for rapid signal transmission and reception. However, Japanese Patent Laid-Open Publication No. H11(1999)-242463 fails to definitely disclose a proper layout of signal wiring and a proper mounting of drive circuits when low voltage differential signals are used in a method for transmitting signals to the drive circuit and for receiving signals from the drive circuit in the liquid crystal display device. Further, Japanese Patent Laid-Open Publication No. H11(1999)-242463 does not give consideration to practical problems which arise when the low voltage differential signals are used and means for overcoming such problems.